Digital cameras are often used in mobile apparatuses, for example in mobile handsets. Recently, camera systems that provide both color and dense depth images have become available. Typically these camera systems comprise at least one infrared image sensor and at least one color image sensor. These camera systems may be used in a variety of new applications in the field of three-dimensional perception. Depth information is typically acquired by using structured infrared light, such as a laser, for projecting a pattern. The projected pattern is then captured by an infrared camera having an infrared sensor. Captured patterns are then used for determining the depth data. The depth data may then be correlated to an RGB camera.
Typically the pattern projected using infrared light is not clearly visible at longer distances. Conventionally this has been addressed by providing an infrared sensor with a band-pass filter passing the band near the used structured infrared light source. Thus, the infrared camera will have a high sensitivity peak around the wavelength of the structured light source. Thus, because of the band pass filter the pattern is visible in an image acquired with the camera. However, if the pattern is formed of a plurality of points, for example, between the points the acquired image consist very little image information.
As there is only very little information between the points the acquired image does not resemble the scene captured. Thus, edges of the objects in the image of the scene are very weak, if visible at all. In other words, the acquired image comprises almost only information that is visible in short distances. Furthermore, if a depth map computed from the pattern is very difficult to map to an image acquired by an RGB-camera when the camera calibration is not known or is inaccurate.